Shaped and structured Pt-3d-transition metal alloy nanocrystals as electrocatalysts for the oxygen reduction reaction

The graphical abstract illustrates the three main shaped or structured Pt-3d-transition metal alloy nanocrystals discussed in this review. It demonstrates different nanostructures’ properties and how they contribute to high ORR activities and catalyst durability. Exemplary of the shape or nanostructure is provided to guide the reader (i.e., octahedron, nanoframes, and nanowires). • The oxygen reduction reaction mechanism on platinum-alloy-based nanocrystal surfaces is introduced in this review. • Synthesis protocols for various shaped and structured Pt-3d-transition metal alloy nanocrystals are extensively discussed. • Developments and advances in oxygen reduction reaction activity and durability of these electrocatalysts are also reviewed. • Outlook and potential challenges in upscaling these nanostructured Pt-based alloys are provided. Proton exchange membrane fuel cells (PEMFCs) have attracted extensive interest in both automotive and stationary applications. However, the drawback hindering the large-scale commercialization of PEMFCs is related to problems such as insufficient power density, high cost, and short operation duration. The major reason for these problems is the sluggish oxygen reduction reaction (ORR) kinetics which takes place on the cathode side of the fuel cell due to the poor catalytic activity and durability of the expensive Platinum (Pt)-based catalyst employed. Subsequently, current research efforts are focusing on the design and development of an advanced Pt-based catalyst that is highly active and durable. As a result, alloying Pt with 3d -transition metals has been known to improve the ORR kinetics, especially of faceted polyhedrons, hollow nanostructures, and one-dimensional nanocrystals. This review therefore focuses on the synthesis protocols of the shaped and structured Pt- 3d -transition metal (Pt-TM) alloys. As such, the synthesis control of the shape/structure, size, and chemical composition of various Pt-TM nano-alloys will be extensively reviewed here followed by a discussion of their electrocatalytic activity as applied in ORR reactions. Lastly, it discusses the outlook on the potential challenges and prospects of shape/structure-controlled electrocatalysts.